1. Field of the Invention
This invention relates to a data recording method and data recording medium that make it possible to suppress the effects of cross-talk by reducing the correlation of recorded data.
2. Description of the Related Art
Currently, optical discs, such as CDs and DVDs, are widely used. In recent years, in addition to CD-DA (CD-Digital Audio), which is a recording medium for reproduction only, CD-R (CD-Recordable), which allows recording digital data only one time, and CD-RW (CD-ReWritable), which allows rewriting digital data a multiple of times, have also come to be used.
When recording data onto or when reproducing data from an optical disc, it is necessary to rotate the optical disc at a specific rpm, and in the case of a recording medium for reproduction only, it is possible to obtain the specified rpm by synchronizing the rpm with the reproduction frequency of the digital data. On the other hand, in the case of a recordable recording medium such as CD-R or CD-RW, there are no digital data initially recorded on the tracks and it is not possible to control the rpm using the same method. Therefore, in the case of a recordable recording medium, the track (group track) that corresponds to the address data wobbles, and the rpm is controlled based on a wobble signal that is read from that track and the address of the track is identified.
Currently, a method of recording an FM modulated wobble signal on the track is known as a method for recording address data that uses wobbling. Also, a method of recording address data on a track by phase modulation of the wobble signal is disclosed in Japanese Laid-open patent application No. H10-69646.
However, there is a demand to further increase the recording density of an optical disc. In order to increase the recording density of an optical disc, it is necessary to reduce as much as possible the spacing between spiral shaped tracks (spacing in the radial direction of the optical disc), however reducing the spot diameter of the laser beam such that it fits completely in the area formed by the track becomes difficult, and a problem exists in that cross-talk from an adjacent tracks occurs.
FIGS. 22A to 22D are figures showing the effect of cross-talk from an adjacent track on the wobble signal. FIG. 22A shows the case when the wobble of the adjacent tracks has the same phase, FIG. 22B shows the case when the wobble of the adjacent tracks has the reverse phase, FIG. 22C show the case when the wobble of the adjacent tracks lags by 90 degrees, and FIG. 22D shows the case when the wobble of the adjacent tracks leads by 90 degrees. FIGS. 22A to 22D, show the effect of the adjacent tracks (track n and track n+2) on the wobble signal for a center track that is indicated as track n+1.
Also, there is a problem in that jitter in the recording clock that is generated by a PLL (phase locked loop) from the wobble increases due to the effect of this kind of cross-talk. The wobble signal is not only used for controlling the disc rotation, but is also used for generating a clock (recording clock) by way of the PLL that becomes a time reference when recording data onto the disk. Therefore, as shown in FIG. 22C or FIG. 22D, for example, when the wobble signal fluctuates in the time-axis direction due to the effect of cross-talk, there is a chance that it will cause jitter in the recording clock.
A method has also been proposed of canceling out cross-talk from the wobble signal. This method detects the cross-talk based on the correlation between the wobble signal from the track being reproduced and the tracks adjacent to that track. In this case, in order to be able to detect the cross-talk, the correlation between the wobble signals is controlled such that it is a minimum. Addresses are normally assigned serial numbers that increase in order incrementally, which gives a strong correlation between addresses of adjacent tracks. Therefore, naturally a strong correlation occurs between the wobble signals of tracks that are modulated and recorded based on the address data. In this method, when there is a strong correlation between addresses, it is not possible to detect the cross-talk accurately. Therefore, it is not possible to reproduce the address data accurately.
In order to solve the problems described above, the object of the present invention is to provide a data recording method and optic recording medium that is capable of reproducing address data accurately by reducing the correlation of address data between adjacent tracks, reducing the effect of cross-talk between adjacent tracks on the recording clock and by making it possible to apply a cross-talk canceller to the wobble signal.